Pressure-testing a 2-stroke - ThumperTalk

 

Thank you for this wonderful information! I wouldn't say guts, rather a lack of brain cells. I'm still learning, I work at a small engine shop but we only service lawn and snow equipment. I have a compression tester at my grandfathers but the thread size is for an automobile spark plug hole, I wonder if I can piece together some adapters at the hardware store to my thread size. I will do my research on a "leak down test" and pull the motor. I suppose this could have burnt up the chrome layer on my piston? I just don't get it because this never happened before, I used to ride it without even a hose clamp on the intake boot all afternoon never had this problem until it started getting colder at night in the late fall, something I did must have caused something to go spontaneously. Great reply's!

 

If it dosen't show the pics and the whole article you need to create an account at thumper talk then you can see everything. When you buy a comp. tester new it comes with at least 2 sizes usually one will fit but with it being at gramp's house there's no telling where the other one is if he's like mine was. Does it have antifreeze in it? Not just water. One of your pics showing the left side of the case has what looks to be mixed fuel around the base gasket on the stator side. Page 8 pic 19

 

Great tutorial looks cheap, but whats the difference between filling air through the intake, or using a gauge on the spark plug and kicking the engine up to PSI (looks easier). Wow are all grandfathers alike seriously? haha I'm not even looking for the other piece, knowing him it's so old that it's metered to only measure larger bores and dosen't read fine compression but who knows.

Yeah plenty of antifreeze it stays topped off which is good considering there was kool-aid in the radiator when I got it, fruit punch I think ...hill billy's sold me the machine. I drained the whole system (hoses, the water jacket, etc,) and filled it up with 50/50 premixed Prestone. I also drained the ATF or differential fluid from the tranny and gave her some Valvoline synthetic 10-50w (used a whole quart just to flush) Ya the friggan expansion pipe kept spitting the exhaust crap out around the flange and all over my motor, it took me several attempts until someone on here recommended I use the black Permatex and it actually worked amazing! Better than any other color or muffler weld (heat activated puddy)

According to wiki "Leak-down testing confines the results to cylinder leakage alone." so if all I have at hand at the moment is a compression tester it's at least a good start to find out if I even need to obtain a leak down tester at all? Assuming they are directly related (you can not have good compression AND a poor leak down rate?)

 

I figured it out, so I'm going to try a compression test, I think your onto something because I just read a bunch of articles about this and now I think I have really low compression because it's fairly easy to kick. I'm just hoping it's blown rings and the sleeve is fine, when I bought it the guy told me in the box of parts there is a brand new sleeve in a good head. He claimed the head was fine on the bike now but continued to explain about redoing the top end and how I should either have someone heavy or drag weights to break in the new head for X amount of hours since I only weight about 115lbs. is this true if I rebuild my top end with the payload?

 

Basically a comp. test determines if A: you are pushing air between the head and cylinder on the upstroke of the piston or B: your're pushing air between the rings and cylinder on the upstroke of the piston. A leakdown test determines if you are sucking air from below the piston on the upstroke of the piston. After a rebuild IE rings, piston, and cylinder bore a proper breakin is crucial to the performance and longevity of the rebuild Cylinder Break In







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You can have good comp. and poor leakdown for example let's say you did a comp. test and you got consistant readings of 200lbs. Yet you do a leakdown test and after 1 min. you have 0. That tells me that the topend ( rings and head ) are good yet there might be a busted base gasket letting air in from under the rings from the vacuum of the leakdown test.

 

Well, I just called my grandfather and he has a compression tester and told me roughly where to find it in his basement. So I guess I will start there, but the only thing that would cause a death rev would be air getting sucked in and not leaking out correct? So the leak down will be crucial. Weighing 115lbs I can probably stand on the kick starter and my body weight will slowly turn it over till I hit the frame on the kick arm.

 

when doing a leak down you may find that the crank seals are bad. a 2 stroke uses positive crank case pressure to work. because yours is running it may not be your problem just something to be aware of. they are not expensive and you can change them without removing the engine.

 

In my other post I meant a busted base gasket would let pressurized air out not a vacuum, it was early. First things first, get ahold of a comp. tester and do 3 readings and see what you got then go from there. If it needs a rebuild which it probably does then you'll need to put a new base gasket on it anyway. Is it smoking more than normal? Are you losing tranny fluid? That would also be an indicater of a bad crank seal.